FR2620575A1 - Antenna for decametre waves, with dipoles and reflector formed by wires - Google Patents

Abstract

The antenna includes aligned pylons P, P', P1-P4 separated by a half-wavelength at the central frequency of use of the antenna. The first P and the last P' pylon have merely a role as support for the reflector R formed by wires; the intermediate pylons P1-P4 serve both as support for the wires of the reflector R and for the radiating dipoles D which are fixed to them. Thus, in order to stretch the wires of the reflector, the pylons are subjected to relatively weak loads regularly distributed between them and also, for each, regularly distributed throughout their height. Application to antennas of medium and high power.

Description

Antenna for HF, dipoles
and reflector formed of wires
The present invention relates to antennas for HF, comprising dipoles placed in front of a reflector formed of parallel wires stretched between pylons.

 Such antennas are ccnnue; they are more particularly used in medium and high power emission.

The known antennas generally consist of two guyed or self-stable pylons between which is stretched a reflector formed by a vertical sheet of horizontal son; this sheet, which is suspended from a catenary stretched between the two pylons, is fixed on one side to one of the pylons and is stretched on the other side by pulley and counterweight systems where the pulleys are hung on the other pylon; the dipoles constitute another layer, which is maintained in front of the reflector by a catenary similar to that of the reflector with insulating assemblies necessary for operation.

These known antennas, an example of which will be described using FIG. 1, have various disadvantages.
the catenaries lead to a general bulk, in width and in height, which is considerably greater than the electrical bulk of the antenna,
the catenaries authorize important deformations of the layers; such deformations cause variations in the input impedance of the antenna which render the antenna unusable from a wind speed always much lower than the maximum speed for which the stability of the antenna is ensured,
the realization of antennas with very large gain becomes delicate given the complexity of the wire structure of the radiating part and the reflector,
the wired structure of the radiating part and the reflector is strongly solicited by the charges constituted by the frost deposits,
- hoisting or lowering an antenna must be done with extreme caution and the intervention in the slicks is a complex operation,
- in terms of their design these antennas are not modular because for each type of antenna it is necessary to redo a study of the forces applied to the stays and pylons,
the improvement of the ratio of the front and rear radiations, ie the reduction of the radioelectric pollution, is done by increasing the density of the wires of the reflector; but these wires, which must be stretched between the two pylons, can not exceed a certain number without bringing unacceptable efforts, especially on the heads of pylons.
The present invention aims to avoid or, at least, to reduce these disadvantages.

 This is achieved, in particular, by using towers on which the dipoles are directly fixed.

 According to the invention an HF antenna comprising dipoles A / 2 (> central wavelength of use of the antenna), two vertical pylons, external and a vertical plane reflector, form of son and arranged between the pylons external, is characterized in that it comprises n vertical pylons (n 'integer greater than zero), between the external pylons, the n + 2 pylons being spaced from A / 2, sn what the dipoles are fixed on the n internal pylons and that the reflector wires are hooked on each of the n + 2 pylons.

The presteve invention will be better understood and other characteristics will appear using the following description and figures relating thereto, which represent:
FIG. 1, an antenna according to the known art,
FIGS. 2 and 3 are front and top views of an antenna according to the invention
- Figures 4, 5 and 6, more detailed views of the elements of the antenna according to Figures 2 and 3.

 In the different figures, the corresponding elements are indicated by the same references.

 FIG. 1 diagrammatically shows, in front view, a 4/6 / 0.5 - 6/7/9/11 MHz antenna according to the prior art>; it is, according to the International Electrical Definition of antennas, an antenna intended to operate in the bands of 6, 7, 9, 11 MHz (which gives about half a wavelength, ss / 2, from 18m to the central frequency of operation) and having 4 groups of 6 dipoles a / 2 superimposed, such as the dipole Di, the lowest dipole of each group being at a height equal to r, 5 A is 18 meters, compared to ground. The groups of dipoles are shifted by 18 meters relative to each other and, in the same group, the dipoles are arranged every 18 meters.

 Two vertical pylons P, P '140 meters high, spaced from each other by 128 meters and whose stays were not shown in Figure 1, serve as a support for the dipoles and a vertical reflector R The reflector R is made of horizontal conductive wires of which only a part has been represented; this reflector is held by a catenary, Cr, and by a set of partially represented cables, fixed to the ground and on the pylon P '; the reflector is subjected to a tensile force towards the pylon P through a set of pulleys, such as A, integral with the pylon P and counterweight, such as B, attached to the end of cables passing through the pulleys; the reflector R thus forms a first vertical ply. Likewise the dipoles, such as Di, form a second vertical ply thanks to a catenary Cd and to a set of cables and insulators partially represented; this second ply is fixed to the ground and on the pylon P 'and is subjected to a tensile force in the direction of the pylon P thanks to the same system of pulleys, cables and counterweights as the first ply.

Spreaders or spreaders, arranged in locations marked T1 to T6, keep the two sheets at a substantially constant distance from one another.

 The antenna according to Figure 1 occupies, between its posts P and P ', a surface of 140 meters high by 128 meters wide.

 The following figures show how, according to the invention, an antenna corresponding to the same international electrical definition can be made in smaller dimensions and avoiding the significant forces to which the antenna supports according to FIG. 1 are subjected.

 FIG. 2 represents an antenna according to the invention, seen from the front. It is a 4/6 / 0.5 - 6/7/9/11 MHz antenna with six pylons, P, P1 A P4, P '. 108 meters high, offset by iN 2 = 18 meters from each other; among these six pylons, two, P and P ', form what may be called external pylons and are not associated with dipoles, while the other four are respectively associated with four groups of six dipoles A / 2, superimposed, such as the dipole D.

A planar reflector R formed of substantially horizontal wires, only part of which has been shown, is hung at the rear of each of the six pylons, which makes it possible to avoid the use of a catenary and reduces the range to 18 meters for each element of wire hanging between two pylons.

 In the example described, the wires are barely tensioned between the pylons since, over a distance of less than 18 meters, given the width of the columns, an arrow of the order of one meter is accepted; this represents a low value, compatible with the forces induced on the pylons by the maximum wind; the deformations of the reflector R under the action of wind and ice, have only a negligible influence on the input impedance of the antenna. Such a structure considerably reduces the voltage stresses to which the pylons, with respect to a structure according to Figure 1; similarly the distribution of forces is continuous over the entire height of the support since the distribution of the son is regular and the absence of catenary avoids the application of very high forces at the top of the pylons. It should be noted in Figure 2, the vertical son, very partially represented which are attached to the horizontal son to maintain the gap between them.

The fixing of the dipoles on the pylons will be specified using the following figures
As shown in FIG. 2, this antenna occupies, between its supports P and P ', an area 118 meters high by 90 meters wide, which is clearly smaller than the corresponding dimensions of the antenna according to FIG. In addition, because the reflector son R are hung between supports very close together it is not necessary to stretch them strongly between their points of support so that their arrow is reduced to an acceptable value.

 FIG. 3 is a diagram, in plan view, of the antenna of FIG. 2. This figure shows that the dipoles such as D and the wires of the reflector R are directly fixed on the pylons P1 to P4. Each pylon, of triangular section, is shrouded at its corners by stays such as Ha, Hd, Hg.

FIGS. 4 and 5 show the pylon P4 with only the dipoles and shrouds associated with it and, for FIG. 5, the reflector R. FIG. 4 shows, in perspective, the pylon P4 which is guyed at three different heights. three front stays, Ha, Hb, Hc, by three right rear stays, Hd, He, Hf, and three left rear stays Hg,
Hh, Hi; these guys, as it is best shown in Figure 5 which is a view from above, are arranged in three vertical half-planes at about 120 degrees from each other; it should be noted that, to avoid the intersections of shrouds, the angle, with respect to the front stays, upright shrouds is slightly different, in absolute value, than that of the shrouds.

left back.

 FIG. 5 also shows a wire of the reflector R, as it is fixed on the rear face of the pylon, whereas the dipoles, such as D, are fixed on the edge opposite this face and are supported by a stay such as H.

The towers P1 to P4 are all identical and the pylons
P and P 'corresponding to pylons P1 to P4 without the dipoles, what has been said or will be said on the pylon P4 can be adapted to the other pylons; likewise, the dipoles being all identical, what has been or will be said on the dipole D is valid for the other 23 dipoles of the antenna described.

FIG. 6 is a perspective view showing the dipole
Figures 4 and 5. This dipole which constitutes an elementary radiating element of the antenna is a dipole A / 2, folded. The dipole is made from metal tubes a horizontal support arm, T, one end of which is secured to the pylon
P4, a rear tube K3, D, K4, horizontal, perpendicular to the arm T and welded in the middle on the other end of the arm T, a front tube, K1, El, E2, K2, parallel to the rear tube and interrupted in an area in the middle and two tubes G1,
G2 forming a short circuit between the front tube and the rear tube to which they are welded, a tube J which extends the tube T towards the interrupted medium of the front tube and on which are fixed, by their tip, two insulators M and N, V-shaped whose ends opposite to the points are respectively secured to the two parts of the front tube surrounding the interruption zone these insulators M and N and the short circuits G1, G2, provide the mechanical rigidity of the dipole.

The interruption zone is the feeding point of the dipole; the two conductors Q1 and Q2 of a power line, Q, end there
The supply line Q of the dipole D is brought back to the ground along the rear of the pylon P4 where it is hung at regularly spaced points, to avoid any displacement; the line could also have been brought to the ground by following the pylon's front ridge or passing inside the pylon.

In this embodiment, each dipole having its own feed line, has, at the base of the pylon, a feed point of its own and it is possible to perform any combination of feeding of the various dipoles in order to to modify the radiation pattern of the antenna; if it is not planned to modify this diagram, the power supply of some dipoles can be done in parallel and the number of access to the foot of the pylons is reduced.

 The stay H provides a mechanical connection between, on the one hand, the point common to the arm T and the front tube, and, on the other hand, the top of the pylon.

 The realization of a folded dipole, according to electrical characteristics to obtain, falls within the field of the prior art; however, the particular mechanical embodiment which has just been described presents certain specific elements specially studied according to the antenna to be produced. Indeed the embodiment according to Figure 6 is a specially opted mounting, graceful to its rigidity, to withstand the forces due to wind and frost.Furthermore it should be noted that the dipole has a vertical plane of symmetry, perpendicular to the plane reflector R and whose trace XX has been indicated in Figure 5 this plane is located in a neutral zone where the potential is zero and the power supply is symmetrical with respect to this plane through the conductors QI and Q2; thus the plane of symmetry may contain metallic conductors (arm T and tube J) which do not participate in the radiation since no current is induced in these conductors; the dipole, from the electrostatic point of view, is connected to the earth by the arm T and the pylon P4.

With respect to the ground plane constituted by the towers with the wires of the reflector R, the dipole is at a distance substantially equal to λ / 4, as shown in FIG. 5. Moreover, the system of two tubes X3, E, K4 and X1, El,
E2, K2 with short-circuits G1, G2 makes the dipole D a thick dipole whose mechanical length, L, as indicated in Figure 5, is less than its electrical length; this allows a spacing of r / 2 pylons according to Figures 2 and 3 without the dipoles of the same level is
The present invention is not limited to the example which has just been described, it is thus, in particular, that the number of pylons carrying dipoles may be less than or greater than 4; the realization of an antenna requires only an implantatior study: on the ground, whatever the number of pylons that it must comprise, from the moment when the modules were made that constitute the external pylons without dipoles , such as P and P ', and internal pylons carrying dipoles, such as P1 ^. P4.

Similarly, the dipoles and the support arms can be made not with tubes but from other types of beams and in particular lattice girders. As for the pylons it is, for example, possible to use 1/8 / 0.5 modules for the 6/7/9/11 MHz frequency bands, ie 8-dipole modules superimposed using pylons. from a height of 154 meters above the ground; such a number of dipoles is very difficult to achieve, at these frequencies, with an antenna of the type of FIG. 1, because of the forces to which the two pylons are subjected to tension the plies of the reflector and the dipoles; it is also possible to associate pylons not all having the same number of dipoles but the antenna then loses its perfectly modular character
The dipoles, such as the dipole D of FIG. 6, could, instead of being horizontal, be rotated at any angle around the tube K3, E, K4.

 The antenna can also be equipped with dipoles> / 2 of conventional type, it being understood that the dipoles described above are particularly well suited to the production of antennas according to the invention, in particular because they do not require to be isolated from their carrier pylons.

 It should also be noted that, in an antenna field, an external pylon such as P or P 'may be common to two adjacent antennas.

Claims (5)

 1. HF antenna with dipoles / / 2 (D) (Central wavelength of antenna utilization), two vertical, external pylons (P, P ') and a vertical plane reflector (R) formed of wires and arranged between the external pylons, characterized in that it comprises n vertical pylons (P1-P4) (n: integer greater than zero) vertical internal, between the external pylons (P, P '), n +2 pylons (P, P ', P1-P4) being spaced from A / 2, in that the dipoles (D) are fixed on the n internal pylons (P1-P4) and in that the reflector wires (R) are hung on each of the n + 2 pylons  2.Antenna according to claim 1, wherein the dipoles (D) are rigid dipoles, folded, vertical plane of symmetry (XX) perpendicular to the plane reflector, characterized in that each dipole (D) is connected by a rigid arm (T) located in its plane of symmetry, at one of the internal pylons (P1-P4) and has two ends located on both sides and in the vicinity of the plane of symmetry, and in that a line power supply (Q), disposed substantially in the plane of symmetry of the dipole, the feeds between its two ends.  3. Antenna according to claim 2, characterized in that each dipole (D) is also connected by a stay (H) to the inner pylon on which it is fixed.  4. Antenna according to any one of the preceding claims, characterized in that the n + 2 pylons (P, P ', P1-P4) are guyed by struts (Ha-Hi) distributed in three vertical half-planes substantially to 120 degrees from each other, one of these planes being perpendicular to the plane reflector (R) and located in front of the antenna.  5. Antenna according to claim 2, characterized in that each dipole (D) has its own power line (Q) and in that this line goes down to the foot of the pylon (P4) which carries the dipole considered.